UMTS Wireless Communication System (3)
Wireless Communications
Problems of UMTS:
Some countries have allocated spectrum
differently from the ITU recommendations,
so that the standard bands most commonly used for UMTS (UMTS-2100) have not
been available. In those countries, alternative bands are used, preventing the
interoperability of existing UMTS-2100 equipment, and requiring the design and
manufacture of different equipment for the use in these markets. As is the case
with GSM900 today, standard UMTS 2100 MHz equipment will not work in those
markets. However, it appears as though UMTS is not suffering as much from
handset band compatibility issues as GSM did, as many UMTS handsets are
multi-band in both UMTS and GSM modes. Penta-band (850, 900, 1700 / 2100, and
1900 MHz bands), quad-band GSM (850, 900, 1800, and 1900 MHz bands)
and tri-band UMTS (850, 1900, and 2100 MHz bands) handsets are becoming
more commonplace.
The early days of UMTS saw problems in many
countries. Overweight handsets with poor battery life were first to arrive on a
market highly sensitive to weight and form factor. The Motorola A830, a debut
handset on Hutchison's 3 networks, weighed more than 200 grams and even
featured a detachable camera to reduce handset weight. Another significant
issue involved call reliability, related to problems with handover from UMTS to
GSM. Customers found their connections being dropped as handovers were possible
only in one direction (UMTS → GSM), with the handset only changing back to UMTS
after hanging up. In most networks around the world this is no longer an issue.
UMTS Releases:
The evolution of UMTS progresses according to
planned releases. Each release is designed to introduce new features and
improve upon existing ones.
§
Release 99
ü Bearer
services
ü 64
kbit/s circuit switch
ü 384
kbit/s packet switched
ü Location
services
ü Call
service: compatible with Global System
for Mobile
Communications (GSM),
based on Universal
Subscriber
Identity Module (USIM)
ü Voice
quality features – Tandem Free
Operation
§ Release
4
ü Edge
radio
ü Multimedia
messaging
ü MExE
(Mobile Execution Environment)
ü Improved
location services
ü IP
Multimedia Services (IMS)
ü TD-SCDMA (UTRA-TDD 1.28 Mcps low chip rate)
§ Release 5
ü IP Multimedia
Subsystem (IMS)
ü IPv6, IP transport in UTRAN
ü Improvements
in GERAN, MExE, etc.
ü HSDPA
§ Release 6
ü WLAN integration
ü Multimedia
broadcast and multicast
ü Improvements
in IMS
ü HSUPA
ü Fractional
DPCH
§ Release 7
ü Enhanced
L2
ü 64
QAM, MIMO
ü Voice
over HSPA
ü CPC –
continuous packet connectivity
ü FRLC
– Flexible RL
§
Release 8
ü Dual-Cell
HSDPA
ü Dual-Cell HSUPA
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